In the process of manufacturing semiconductor devices, various processing apparatuses are used for performing processes, such as film-deposition, oxidation, diffusion, reformation, annealing, and etching, on a target substrate, such as a semiconductor wafer. A vertical heat-processing apparatus for simultaneously heat-processing a number of wafers is known as a processing apparatus of this kind.
FIG. 7 is a sectional view showing a conventional rotation mechanism for rotating a wafer boat, employed in a vertical heat-processing apparatus. As shown in FIG. 7, a rotation mechanism 115 is disposed on a lid 105, which is movable up and down to open and close the furnace port (load port) of a vertical heat-processing furnace. The rotation mechanism 115 is used for rotating a wafer boat (holder), which holds a number of wafers (target substrates) thereon.
The rotation mechanism 115 includes a rotary shaft 116, and a support unit 119 that supports the rotary shaft 116 rotatably through a bearing 117 and a sealing member 118. The bottom end of the rotary shaft 116 is connected to a motor 128 through a belt 130. The top end of the rotary shaft 116 penetrates the lid 105 and is connected to a turntable 120. The turntable 120 is formed of a lower member 120a and an upper member 120b detachably attached to each other. A labyrinth structure 160 is formed between the peripheral portion of the turntable 120 and the lid 105, to prevent a process gas in the furnace from entering the clearance gap between the turntable 120 and lid 105 and leaking therefrom.
A structure for cooling the rotary shaft 116 is adopted to prevent the durability of the bearing 117 and sealing member 118 from lowering due to heat from the heat-processing furnace. In this cooling structure, an inactive gas (for example, nitrogen gas N2) flows around the rotary shaft 116, and cooling water circulates through a cooling passage 132 formed near the center of the lid 105, so that the rotary shaft 116 is cooled by the inactive gas and cooling water. The inactive gas is supplied into the clearance gap between the support unit 119 and rotary shaft 116 above the sealing member 118, and flows through the clearance gap between the turntable 120 and lid 105 into the inside of the furnace. The cooling passage 132 is formed near the center of the lid 105 to have an annular shape surrounding the rotary shaft 116. The cooling water is supplied into one end of the cooling passage 132 and is exhausted from the other end.
The vertical heat-processing apparatus is designed to bear a certain high temperature of, e.g., about 1000° C. in a heat process. However, where it is used at a higher temperature of, e.g., about 1200° C. in a heat process, the conventional cooling structure cannot provide sufficient cooling. As a consequence, for example, the rotary shaft 116 and bearing 117 cling or thermally stick to each other due to thermal expansion, whereby the bearing 117 and sealing member 118 may be damaged or lowered in durability.
The rotary shaft 116 is usually made of zirconia, which is a material with a low thermal conductivity, and thus it tends to accumulate heat conducted from the inside of the furnace, and is difficult to cool. Furthermore, the clearance gap S between an axial hole formed in the lid 105 and the rotary shaft 116 is as large as, e.g., 1 mm, thus it is difficult to sufficiently cool the rotary shaft 116 from the cooling passage 132.